Does a car speedometer measure speed, velocity, o*rwe26o 4rlho ,; iqqcr both?

Can an object have a varying speed if its velom kmcd5j +vyo( 59f2jwcity is constant? If yes, give examkwv9djj +5m(yo 2cfm 5ples.

When an object moves with constant vel,ijt2ejj+ c7t11xwt/ lb5k t7;. lsj/hl cilhocity, does its average velocity during any time interval differ from its instantaneous vell, .h /+2 7tj thl cwit5/clsbkie;l1j7tj 1jxocity at any instant?

In drag racing, is it possible for the car with the greatest spee0c )4gs9,k yxhb- sbibst 7v yz;*dwi5d crossing the f i)k 5b0 t*ysvb9xg,zw;h-cy is7sbd4inish line to lose the race? Explain.

If one object has a greater speed than a second object, dm1 34zq i1o xsb,syz5joes the first necessarily have a greater acceleration? Explai1m,z zb s5x13oy4qjisn, using examples.

Compare the accelerator d,egkx;7d 3ion of a motorcycle that accelerates from 80km/h to 90km/h with the acceleration of a bicycle that accelerates from rest to 1odxk g;7, 3dre0km/h in the same time.

Can an object have a northward velocity and a southward acceleratom kj0z6oq8vo: :1djpion? Explain.

Can the velocity of an object be negative when its acc(p -gqpy 4pm;b pm ;)b0(tmsdveleration is positive? What about vice versa? gm (p;;dbp( 0)vmq4pt-pmsyb

Give an example where both the velocity and accelerationix:41oryt 7gi are negative.

Two cars emerge side by side from a tunnel. Car A is traveling with a sprkq2hqke66 q: eed of 60km/h and has an acceleration of 40km/h/min . Car B has a speed of 40 km/h and has an acceleration of 60km/h/min . Which car is passing the othq2kq6 r 6k:eqher as they come out of the tunnel? Explain your reasoning.

Can an object be increasing in speed as its acceleration decr x152e-f ri7( dgnk0m+dxnluhc5ln- heases? If so, give an example. If not, explain.nkr-ncu l 2i51edl0 hnxd- (x7ghm5+f

A baseball player hits a foul ball straight up into the air. It leaves bla(b)u9sg .a the bat with a speed of 120km/h . In the absence of air resistance, how fast will the ball be tr9 sb.(u)g aablaveling when the catcher catches it?

As a freely falling object speeds up, what is happ q+sni82wirivu/5. zvqc4v+f ening to its acceleration due to gravity — doe8 v+i+s /4zv 2rqfqiwvc i.nu5s it increase, decrease, or stay the same?

How would you estimate the maximum height you could throw a ball verct/g82+el ;8 mh kj4ao8alsvjtically upward? How would you estimate the maximum speed j;ca+2s ta8 l488j hkml /eovgyou could give it?

You travel from point A to point B in a car moving at a constant v8a5ascp2ob( speed of Then you travel the same distance from point B to another point C, moving at a constant speed of 90km/h . Is your average speed facv8ap5sob2 ( or the entire trip from A to C 80km/h ? Explain why or why not.

In a lecture demonstration, a 3.0-m-long vertical string with ten bolt*penx:6/ 9xfnyu5hejx bfw :s 2/7 qjzs tied to it at equal intervals is dropped from the ceiling of the lecture hall. The string fallu /:*y : befejjp7qxnhn5x/f9x w6z2ss on a tin plate, and the class hears the clink of each bolt as it hits the plate. The sounds will not occur at equal time intervals. Why? Will the time between clinks increase or decrease near the end of the fall? How could the bolts be tied so that the clinks occur at equal intervals?

Which one of these motions is no)reixh s (+skb q2t1npy,: ly h+1k7qkt at constant acceleration: a rock falling from a cliff, an elevator moving from the second floor to the fifth floor making stops along the way, a dish restipx)q:yhkk+tl 7 ,s1+r2(y kq1n sebhing on a table?

An object that is thrown vertically upward will return to its original posit/ fc)b8p f g5.;;z;f(ghrbflz: vpknxion with the same speed as it had initially if air resistance is negligible. If air resistance is appreciable, will this result be altered, and if so, how? [Hint: The acceleration due to air resistance i rczb8h);ngf; (f;l/zgkp 5 xf.vf:bp s always in a direction opposite to the motion.]

Can an object have zero velocity and nonzero acceleration tc7ljqrpu/3e*yu0grbe oa6r5 ;) d*u;6 f pvs at the same time? Give exampd7ceg ap/pf;q*ls ujerr 5t*y6 0bu)rvuo3 ;6les.

Can an object have zero acceleration and nonzero velocity ig 7xr1b8wbf 4 2cqep:at the same time? Give e cbw1ep:8qf4bigr72x xamples.

Describe in words the motion plotted in Fig. 2–23z,1 uj6j jxo1*l)rs;or njhjik-e:v 8 in terms of v, a, etc. [Hint: First try to duplicate the motion plottedievr k *;j x )u-o16j3j1 :jsl,norjhz by walking or moving your hand.]

Describe in words the motion of e*,vpc-nbs1ld;xq ni7ciy5(qyj v5*the object graphed in Fig. 2–29.

  What must be your car’s average speed bn pnw2yd-6/s in order to travel 235 km in 3.25 h?    km/h

  A bird can fly 25 km/h How long does it take to fly 15 km? 4os) sze ja r 5h*n2fu4jd09id   h

  If you are driving along az4 1fdag. kv/k straight road and you look to the side for 2.0 s, how far do you travel during this inattentive perdv.f/k4gz1ak iod?    m

  Convert 35 mi/h to a4jsq 6;ygxn2va (so 0
(a) km/h,    km/h
(b) m/s ,    m/s
(c) ft/s.    ft/s

  A rolling ball moves from gm 391:9i:fj c6b(dyk.t qr2ogq xl v7 9tuewt$x_1$ = 3.4 cm to $x_2$ = -4.2 cm during the time from $t_1$ = 3.0 s to $t_2$ = 6.1 s What is its average velocity?    cm/s

  A particle at $t_1$ = -2.0 s is at $x_1$ = 3.4 cm and at $t_2$ = -4.5 s is at $x_2$ = 8.5 cm What is its average velocity? Can you calculate its average speed from these data?    cm/s

  You are driving home from school steadily atnu 4 4qp-q)aaz 95 km/h for 130 km. It then begins to rain and you slow to 65 km/h You arrive home after4apq4nz-uq a) driving 3 hours and 20 minutes.
(a) How far is your hometown from school?    km
(b) What was your average speed?    km/h

  According to a rule-of-thumb, every five seconds between a lightn)zsbz*2 c3owm+;ayx aing flash and the following thunder gives the distance to the flash in miles. Assuming that the flash of light arrives in essenti+*w2 bc3)zaz;xsmay oally no time at all, estimate the speed of sound in m/s from this rule.    m/s

  A person jogs eight complete laps around a quarter-mile trac-z 1 kcy/efy,vx ;bp)jivj5,ck in a total time ofb/,xj- ;vvekyif cpy ,)j1 cz5 12.5 min. Calculate
(a) the average speed    m/s
(b) the average velocity, in    m/s

  A horse canters away from its trainer iqj;cvm9at u492yav d3-j;mltn a straight line, moving 116 m away in 14.0 s. It then turns abruptly and gallops hv;tl943ya2d 9;c -am tmquv jjalfway back in 4.8 s. Calculate
(a) its average speed    m/s
(b) its average velocity for the entire trip, using “away from the trainer” as the positive direction.    m/s

  Two locomotives approach each other on paralt/h+ x*2 x(rpo .saofmlel tracks. Each has a speed of 95 km/h with respect to rs*h(. 2pt+xoamo f/xthe ground. If they are initially 8.5 km apart, how long will it be before they reach each other? (See Fig. 2–30).    min

  A car traveling 88 km/h is 110 m behiv6 rezqnpm2h /k+-ma) nd a truck traveling How long will it take the car to rea)a /pknqrmhz -2+6vm ech the truck?    s

  An airplane travels 3100 km at a speed of 790 km/h , and then encount+3ks3hq:fkrx ers a tailwind that boosts its speed to 990 km/h for the :+kqfr3hkx s3next 2800 km.
What was the total time for the trip?    h
What was the average speed of the plane for this trip? [Hint: Think carefully before using Eq. 2–11d.]    km/h

  Calculate the average spee8(e3 id1 vtoqyz48l qxd and average velocity of a complete round-trip in which the outgoing 250 km is covered at 95 km/h followed by a 1.0-hour lunch break, and the return 250 km is cy3t8qoi xq 4vd8lz1( eovered at 55 km/h.    km/h

  A bowling ball traveling with1qp ( z5 yb:rjng geyb8mv:k/pj4.f( f constant speed hits the pins at the end of a bowling lane 16.5 m long. The bk4fn(bgj pm z5rbg /evfp1 :(:.8yjyqowler hears the sound of the ball hitting the pins 2.50 s after the ball is released from his hands. What is the speed of the ball? The speed of sound is 340 m/s.    m/s

  A sports car accelerates from rest to 95 km/h in 6.2 s. What is its avroq5wdeq45 m1 erage acceleration55de1w mq4o qr in $m/s^2$ ?    $m/s^2$

  A sprinter accelerates from rest to 10.0 m/s in 1.35 s. What is her acxg o.q q7 in+ac4)4mymceleration mn74 iq) yo.4mq+cgxa
(a) in $m/s^2$ ,    $m/s^2$
(b) in $km/h^2$ ?    $km/h^2$

  At highway speeds, a particular automobile .lpgonv btgo-)7t9;iis capable of an acceleration of abou. itlbtognp7 g9o)v ;-t $1.6 m/s^2$ At this rate, how long does it take to accelerate from 80 km/h to 110 km/h ? $\approx$    s (Round to the nearest integer)

  A sports car moving at constant speed travels 110,l+*rkd- uf9:k6we( wwjgss g m in 5.0 s. If it then brakes and comes to a stop in 4.0 s, what is it-*kj :u s w+deg6wgkl,s(9rwf s acceleration in $m/s^2$ ? Express the answer in terms of “g’s,” where 1.00 g = 9.80 $m/s^2$ .    $m/s^2$    g's

The position of a racing car, which starts from rest at t = 0 and moves i; -glylct1 ,ytn a straight line, is given as a function of time in the follo yytlt;1lg,c-wing Table. Estimate (a) its velocity and (b) its acceleration as a function of time. Display each in a Table and on a graph.

  A car accelerates from 13 m/s to2 yspt 2ayo jk*r0,dpu+fwpl 924 hgw1 25 m/s in 6.0 s. What was its acceleration? How far did it travel in this yo2t h9dpk 0j y2p+g12ap* ur wl4,fwstime? Assume constant acceleration.    $m/s^2$    m

  A car slows down from 23 m/s to rest in a distance of 8a5 )1)0f 3:ercuwdl;vv m p4xzedn)xa5 m. What was its acceleration, assumed co 5drx:m;a wa pe0)ulvv4 c)zen1)3fdxnstant?    $m/s^2$

  A light plane must reac q7-m j)tin98cotsuye)envk2)py8 1 n:b qc0mh a speed of 33 m/s for takeoff. How long a runway is needed if the (constant) acceleyqmo nu i91e2m8jyc -pv)80)t)q 7 :nsbtnkecration is $3.0 m/s^2$ ?    m

  A world-class sprinter can burst out of th i4mb 8odcygmg6h4rk;j,t,x ;e blocks to essentially top speed (of about 11.5 m/s) in the first 15.0 m of the race. What is the average acceleration of this sprinter, and how long does it take her to4;4 ,tkgh,imyb 86dmgx;j cro reach that speed? $\approx$ =    $m/s^2$ (retain two decimal places)    s

  A car slows down uniformly from a speed of 12.0 m/s to rest in 6.00 s. How f2s1z.w.jvv y far did it travel in f. vyz.1wjs2v that time?    m

  In coming to a stop, a car le,m(n.u;vx/.4pw q0dks bv uhv aves skid marks 92 m long on the highway. Assuming a deceleratksqh,v;/x bm.nu vw( d04v.up ion of $7.00 m/s^2$ estimate the speed of the car just before braking.    m/s

  A car traveling 85 km/h strikes a tree. The front end of th,(zom/tm.h b6voe ajggs kg a6* l:(g/e car compresses and the driver comes to rest after traveling 0.80 m. What was the average acceleratg 6m js k vt(abeo,(:ag6./gzh/gol*mion of the driver during the collisi on? Express the answer in terms of “g’s,” where 1.00 g = 9.8 $m/s^2$ . =    $m/s^2$ (retain two decimal places )    g’s

  Determine the stopping distances for a car with an initial ) soha)4t7d: ge jicd)speed of 95 km/h and human reaction time of 1.sji edtcg:)74h oa))d 0 s, for an acceleration
(a) a = -4.0 $m/s^2$ ;    m
(b) a = -8.0 $m/s^2$    m

Show that the equation;g5efdf tg )*r for the stopping distance of a car is $d_S\,=\,v_0t_R\,-\,{v_0}^2/(2a)$ , where $ v_0$ is the initial speed of the car, $ t_R $ is the driver’s reaction time, and a is the constant acceleration (and is negative).

A car is behind a truck going 25 mkxwy0tp -/l l0/s on the highway. The car’s driver looks for an opportunity to pass, guessing that his car can accelerate at 1.0 0tx0 l yklwp-/$m/s^2$ He gauges that he has to cover the 20-m length of the truck, plus 10 m clear room at the rear of the truck and 10 m more at the front of it. In the oncoming lane, he sees a car approaching, probably also traveling at 25 m/s He estimates that the car is about 400 m away. Should he attempt the pass? Give details.

A runner hopes to complete the 10,000-m run in less than 30. k(,hn jtr:lc(ef61kqi0ew a,0 min. After exactly 27.0 min, there acrl:i( 0enqkjf6,( ,w eat1khre still 1100 m to go. The runner must then accelerate at 0.20 $m/s^2$ for how many seconds in order to achieve the desired time?

A person driving her car at 45 km/h approacn1.4)p sd iah.l 3gh4 )y t.ylt2vmsythes an intersection just as the traffic light turns yellow. She k.tsla.gl yn44 3sm hd .vpty12iyht))nows that the yellow light lasts only 2.0 s before turning red, and she is 28 m away from the near side of the intersection (Fig. 2–31). Should she try to stop, or should she speed up to cross the intersection before the light turns red? The intersection is 15 m wide. Her car’s maximum deceleration is $-5.8 m/s^2$ , whereas it can accelerate from 45 km/h to 65 km/h in 6.0 s. Ignore the length of her car and her reaction time.

  A stone is dropped from the top of a cliff. It hix pwxk.f ,keu*u+gu (0v9 miv)ts the ground below after 3.25 s. Hopm)k evu x+u gk*x v.,9(w0iufw high is the cliff?    m

  If a car rolls gently wx6 un4u d(qp:($v_0\,=\,0$) off a vertical cliff, how long does it take it to reach 85 km/h ?    s

  Estimate
(a) how long it took King Kong to fall straight down from the top of the Empire State Building (380 m high), $\approx$ =    s (retain one decimal places)
(b) his velocity just before “landing”?    m/s

  A baseball is hit nearly1dm h gd*x9axf j.al.c.)m6ap straight up into the air with a speed of 22 m/s
(a) How high does it go?    m
(b) How long is it in the air?    s

  A ballplayer catches a bldk ;01g3hf w ndbh.1rall 3.0 s after throwing it vertically upward. With what speed did he throw it, and what frnkh l31b01dw;d gh.height did it reach?    m/s (Round to the nearest integer)    m

An object starts from,r8v/h0 /p-+qrk:zqr 2tuvgua 3 ew6u 5fzo xw rest and falls under the influence of gravity. Draw graphs of (a) its speed and (b) the disv6uz-zq8: +5up2/t e/3gu0o,krwxawrq vfrh tance it has fallen, as a function of time from t = 0 to t = 5.00 s . Ignore air resistance.

A helicopter is ascending vertically with a speed re2g) rm+epv5of 5.20 m/s. At a height of 125 m above the E) 2mre5p re+gvarth, a package is dropped from a window. How much time does it take for the package to reach the ground? [Hint: The package’s initial speed equals the helicopter’s.] t =__ s

For an object falling freely from rest, show that the dxec 4p;,*itte6qqrf1 istance traveled during each successive second increases in the ratio of successive odd integers (1, 3, 5, etc.). This was first showe,x r4tt1;if6 p qc*qen by Galileo. See Figs. 2–18 and 2–21.

If air resistance is neglected, show (algebraically) that a ball thrown vertz rt3pzt.n5+n za)re2 c*mbggo 71kh: ically upward with a speed aeg h z c)t:p+37znz1o .ntbg*rr2 5km$v_0$ will have the same speed, $v_0$, when it comes back down to the starting point.

  A stone is thrown vertically upward with a sia6o1(x t( :r(sci9*n vi*-aq;wvjp2 ndigsypeed of 18.0 m/s
(a) How fast is it moving when it reaches a height of 11.0 m? |v| =    m/s
(b) How long is required to reach this height? t =    s,    s
(c) Why are there two answers to (b)?

  Estimate the time between each photoflas5 jx :w2yisbpt6*mk*v h of the apple in Fig. 2–18 (or number of photoflashes per second). Assume the apple is about 10 cm in diameter. [Hint: Use two apple positions, but not the unclear onmisvjt*wx: 6y52pkb* es at the top.]
T =    s
   flashes per second

  A falling stone takes 0.28 s to travel past a window 2.2 m tall 2msi.edc rj40 (Fig. 2–32). From what height above de 2s0ij .mr4cthe top of the window did the stone fall?    m

  A rock is dropped from a sea cliff, an ; twco,lfxno7ka g81z :w5(qrd the sound of it striking the ocean is heard 3.2 s lat8n 7x5octak;zww q (,rgflo1:er. If the speed of sound is 340 m/s , how high is the cliff? H =    m

  Suppose you adjust youfk2 pvi m)bg5h 3(uer-i-gnf/r garden hose nozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 m above the ground (Fig. 2–33). When you quickly move the nozzle away from the vertical, you hear the water striking the ground nexrb23i)fg-5g uf(-h kipenmv/ t to you for another 2.0 s. What is the water speed as it leaves the nozzle?    m/s

  A stone is thrown vertically upward with a speed of 12.0 m/syx 0scz-ifz )+ from the edge of a cl -+cyxz sfz0)iiff 70.0 m high (Fig. 2–34).
(a) How much later does it reach the bottom of the cliff? t =    s
(b) What is its speed just before hitting?    m/s
(c) What total distance did it travel?    m

  A baseball is seen to pass upward by a window 28 m abovn.rl - b(u1ywae the street with a vertical speed of 13 w .rn-ybl 1a(um/s If the ball was thrown from the street,
(a) what was its initial speed,    m/s
(b) what altitude does it reach,    m
(c) when was it thrown,    s
(d) when does it reach the street again?    s

Figure 2–29 shows the velocity of a train as a funxmr95n x9he z cd.9d3oction of time. (a) At what time was its velocity greatest? (b) During what periods, if any, was the velocity constant? (c) During what periodsxdm 9enx9od39.c5h zr , if any, was the acceleration constant? (d) When was the magnitude of the acceleration greatest?

  The position of a rabbit along a straight tunnel as a function ydjo-ruq 9 37yof time is plotted in Fig. 2–28. What is its instantaneous velocitu-qroy j79dy 3y
(a) at t = 10.0 s    m/
(b) at t = 30.0 s What is its average velocity    m/s
(c) between t = 0 and t = 5.0 s    m/s
(d) between t = 25.0 s and t = 30.0 s    m/s
(e) between t = 40.0 s and t = 50.0 s ?    m/s

  In Fig. 2–28,
(a) during what time periods, if any, is the velocity constant? t =    s to t $\approx$    s
(b) At what time is the velocity greatest? t =    s
(c) At what time, if any, is the velocity zero? t =    s
(d) Does the object move in one direction or in both directions during the time shown?

  A certain type of automobile can accelerate approximately as shown i,r; xn j6 sxq 1n+bb(fvhtdr.+n the velocity–time graph of Fig. btnnhvxr.,+ f qdrj;b+61(xs 2–35. (The short flat spots in the curve represent shifting of the gears.)
(a) Estimate the average acceleration of the car in second gear and in fourth gear. The average acceleration in $2^{nd}$ gear is given by    $m/s^2$ The average acceleration in $4^{th}$ gear is given by    $m/s^2$
(b) Estimate how far the car traveled while in fourth gear.    m

  Estimate the average acceleration of the car in cado hw*8h jee8+)t9 pthe previous Problem (Fig. 2–35) when iph9h 8)+te waod*8ecjt is in
(a) first,    $m/s^2$
(b) third,    $m/s^2$
(c) fifth gear.    $m/s^2$
(d) What is its average acceleration through the first four gears?    $m/s^2$

  In Fig. 2–29, estimate the distance the object srl9a-6q wv d1traveled during
(a) the first minute,   
(b) the second minute.    m

Construct the vs. t graph for the object whose h kl9e;nic;1q gt c 023u.zxc7vqm,uvdisplacement as a function of time is given by Fig. 2–2803c7 2t9ln gez; xv 1cquv.,hicmuqk;.

Figure 2–36 is a position versus time graph for the motion c1/)h2hw-tujoq,ku:gw p,e b)+xspr of an object along the x axis. Consider the time interval from A to B. (a) Is the object moving in the positive or negative direction? (b) Is the object speeding up or slo1- ):cphebu2s),q+wu /ktjwhr xg,powing down? (c) Is the acceleration of the object positive or negative? Now consider the time interval from D to E. (d) Is the object moving in the positive or negative direction? (e) Is the object speeding up or slowing down? (f) Is the acceleration of the object positive or negative? (g) Finally, answer these same three questions for the time interval from C to D.

  A person jumps from a fourtox i 9jh/ +c/xfzr*/ryh-story window 15.0 m above a firefighter’s safety net. The survivor stretches the nei9//hjcr fox*r+/ yzxt 1.0 m before coming to rest, Fig. 2–37.
(a) What was the average deceleration experienced by the survivor when she was slowed to rest by the net?    $m/s^2$
(b) What would you do to make it “safer” (that is, to generate a smaller deceleration): would you stiffen or loosen the net? Explain.  ----待选择----stiffen loosen 

The acceleration due to gravity on the Moon is about one-sixth what it is on Ebzr zl :e xoe9)15owe+arth. If an object is thrown vertically upward on the Moon, how many times higher will it go than it wouldw9z xoerbo e z1e:l)5+ on Earth, assuming the same initial velocity?

  A person who is properly constrained by an over-the-shoulder seat sjpo,25ld 4yno2ab 79kuqdw(belt has a good chance of surviving a car collision if the decelerati lu429 2y,donobdpqj5w 7a(s kon does not exceed about 30 “g’s” $(1.0 g\,=\,9.8\,m/s^2)$. Assuming uniform deceleration of this value, calculate the distance over which the front end of the car must be designed to collapse if a crash brings the car to rest from 100 km/h . $\approx$    m(retain one decimal places)

  Agent Bond is standingunh37li0p/fz g/ y gv. on a bridge, 12 m above the road below, and his pursuers are getting too close for comfort. He spots a flatbed truck approaching at 25 m/s , which he measures by knowing t / .hp0i3y7fzgn/ug vlhat the telephone poles the truck is passing are 25 m apart in this country. The bed of the truck is 1.5 m above the road, and Bond quickly calculates how many poles away the truck should be when he jumps down from the bridge onto the truck to make his getaway. How many poles is it?    poles

  Suppose a car manufactq u.,a n6xbj;k h7ko.kurer tested its cars for front-end collisions by hauling them up on a crane and dropping them from a certain heighu.7;bahk6o .jnq k,xkt.
(a) Show that the speed just before a car hits the ground, after falling from rest a vertical distance H, is given by $\sqrt{2gH}$ . What height corresponds to a collision at
(b) 60 km/h ? $\approx$    m (Round to the nearest integer)
(c) 100 km/h ? $\approx$    m (Round to the nearest integer)

  Every year the Earth travels abf;9par*lkeurg,b5 gf93 il+mout $10^9\,km$ as it orbits the Sun. What is Earth’s average speed in km/h?    $ \times10^{ 5}\,km/h $

  A 95-m-long train begins uniform acceleration fros.d2jjagx 6ws 6;:jium rest. The front of the train has a speed of 25 m/s when it passes a railway worker who is standing 180 m from where the front of the train started. What will be the speed of the last car as it passes the worker? (See6s;j .x:sai jju d6wg2 Fig. 2–38.)    m/s

  A person jumps off a divifi qxkg/a7cd,4 .,s39dsgi z kng board 4.0 m above the water’s surface into a deep pool. The person’,d. sz g3,7kxq iag9ic dkf/s4s downward motion stops 2.0 m below the surface of the water. Estimate the average deceleration of the person while under the water. $\approx$    $m/s^2$ (Round to the nearest integer)

  In the design of a rapid transit system, it is necessary to e 1p* uf w76q.t n6:wfay)ssgybalance the average speed of a train against the distance between stops. The more stops there are, the slower the train’s average speed. To get an idea of this problem, calculate the time it takes a train to m)eqw :7s6ynu f pgf tw*6sy1.aake a 9.0-km trip in two situations:
(a) the stations at which the trains must stop are 1.8 km apart (a total of 6 stations, including those at ends);    min
(b) the stations are 3.0 km apart (4 stations total). Assume that at each station the train accelerates at a rate of $1.1 m/s^2$ until it reaches 90 km/h then stays at this speed until its brakes are applied for arrival at the next station, at which time it decelerates at $-2.0 m/s^2$ Assume it stops at each intermediate station for 20 s.    min

  Pelicans tuck their wingmqxz h *4hr0lfh :2k*rs and free fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 16.0 m and cannot change 0 q2r*h*h:rkfzm h x4lits path once committed. If it takes a fish 0.20 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.    m

  In putting, the force with which a golfer strikes a ball is plabz):vv.ixwju0p;f*r nned so that the ball will stop within some small distance of the cup, say, 1.0 m long or short, in case the putt is missed. Accomplishing this from an uphill lie (that is, putting downhill, see Fig. 2–39) is more difficult th: zjf)0;ivbpw.x*r vuan from a downhill lie. To see why, assume that on a particular green the ball decelerates constantly at $20 m/s^2$ going downhill, and constantly at $3.0 m/s^2$ going uphill. Suppose we have an uphill lie 7.0 m from the cup. Calculate the allowable range of initial velocities we may impart to the ball so that it stops in the range 1.0 m short to 1.0 m long of the cup.    m/s to    m/sDo the same for a downhill lie 7.0 m from the cup.    m/s to    m/sWhat in your results suggests that the downhill putt is more difficult?

  A fugitive tries to hop on a freigea1goxx*a , x.ht train traveling at a constant speed of 6.0 m/s Just as an empty box car passes him, the fugitive 1 axo,g*.xxaestarts from rest and accelerates at $a\,=\,4.0 m/s^2$ to his maximum speed of 8.0 m/s
(a) How long does it take him to catch up to the empty box car?    s
(b) What is the distance traveled to reach the box car?    m

  A stone is dropped from the roof of a high builjx-+ ze mk : p uf2j6.p4mug*rym:m;fyding. A second stone is dropped 1.50 s later. How far apart are the stones whenxmfj.2p gm*jrumyfm6 y ep: 4;:+- uzk the second one has reached a speed of 12.0 m/s ?    m

  A race car driver must avn6t od vf3ikwuz2(va4h76i)aerage 200.0 km/h over the course of a time trial lasting ten laps. If the first nine laps were done at 198.0 km/h . what average speed must be maintained for the a)7vi i4od thwu26kv 3afnz(6 last lap?    km/h

  A bicyclist in the Tour de France crests a mountain pass as he moves-su: .90tir5)j giio mrqon1f at 18 km/h . At the bottom, r1 -q0 inr: .so5uot f9iimj)g4.0 km farther, his speed is 75 km/h . What was his average acceleration (in $m/s^2$) while riding down the mountain?    $m/s^2$

  Two children are playing on two trampolinesqm z1pes )dus+8 0q54vdii8 qc. The first child can bounce up one-and-a-half times higher than the second child. The initial 5vz 84qis+)0qu id s qepcd1m8speed up of the second child is $5.0 m/s $.
(a) Find the maximum height the second child reaches. $\approx$    m(retain one decimal places)
(b) What is the initial speed of the first child? $\approx$    m/s(retain one decimal places)
(c) How long was the first child in the air?    s

  An automobile traveling 95 km/h overtakes a 1;)*-1ovz ie;gt os pge.10-km-long train traveling in the same direction on a track parallel to the road. If the train’s speed is 75 km/h . how long p;g ove*e-tg1s;zoi )does it take the car to pass it, and how far will the car have traveled in this time? See Fig. 2–40. What are the results if the car and train are traveling in opposite directions? t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places) t =    min The distance the car travels during this time is $\approx$    km(retain one decimal places)

  A baseball pitcher throws a baseball with )u v+woatd8vbfw3y yp+a,m;mh d7,c 8 a speed of 44 m/s In throwing the baseball, the pitcher7 fmv)u awmp 8wod+y;3d+ bhv aytc8,, accelerates the ball through a displacement of about 3.5 m, from behind the body to the point where it is released (Fig. 2–41). Estimate the average acceleration of the ball during the throwing motion.    $m/s^2$

  A rocket rises verticalp2hw )oc)cy n-t ;8wktly, from rest, with an acceleration of $3.2 m/s^2$ until it runs out of fuel at an altitude of 1200 m. After this point, its acceleration is that of gravity, downward.
(a) What is the velocity of the rocket when it runs out of fuel? $\approx$ =    m/s(Round to the nearest integer)
(b) How long does it take to reach this point? $\approx$ =    s(Round to the nearest integer)
(c) What maximum altitude does the rocket reach?    m
(d) How much time (total) does it take to reach maximum altitude? $\approx$ =    s(Round to the nearest integer)
(e) With what velocity does the rocket strike the Earth?    m/s
(f) How long (total) is it in the air?    s

  Consider the street pattern shown in Fig. 2–42. Eac4ox9 ntf o,zf;9baqu2h intersection has a traffic signal, and the speed limit is 50 km/s . Suppose you are driving from the west at the speed limit. When you are 10 m from the first intersection, all the lights tur4ot9 x;o zfanuq ,f2b9n green. The lights are green for 13 s each.
(a) Calculate the time needed to reach the third stoplight. Can you make it through all three lights without stopping?  ----待选择----yesno 
(b) Another car was stopped at the first light when all the lights turned green. It can accelerate at the rate of $2.0 m/s^2$ to the speed limit. Can the second car make it through all three lights without stopping?  ----待选择----yesno 

  A police car at rest, passed by a speeder trahhd0db gz (qt,09hce 8veling at a constant 120 km/h takes off in hot pursuit. The police officer catches up to the speeder in 750 m, maintaining a constant acceleration.ze8dc, hqbtdh0hg 0 9(
(a) Qualitatively plot the position vs. time graph for both cars from the police car’s start to the catch-up point. Calculate
(b) how long it took the police officer to overtake the speeder, $\approx$ =    s(Round to the nearest integer)
(c) the required police car acceleration, $\approx$ =    $m/s^2$(Round to the nearest integer)
(d) the speed of the police car at the overtaking point. $\approx$ =    m/s(Round to the nearest integer)

  A stone is dropped from the roof of a bu,tbdu ;v9q2ex49x p xz*kub3 ailding; 2.00 s after that, a second stone is thrown straight down with an initial speed of 25.0 m/s x9q*bv 3x9,pb4 kudex2a;t zu and the two stones land at the same time.
(a) How long did it take the first stone to reach the ground? $t_1$ =    s
(b) How high is the building?    m
(c) What are the speeds of the two stones just before they hit the ground? #1    m/s #2    m/s

  Two stones are thrown valmebucier+y7o 648: ertically up at the same time. The first stone is thrown with an initial velocity of 11.0 m/s from a 12th-floor balcony of a building and hits :4emabeliu6 y8 c ro7+the ground after 4.5 s. With what initial velocity should the second stone be thrown from a $4^{th}$-floor balcony so that it hits the ground at the same time as the first stone? Make simple assumptions, like equal-height floors.    m/s

  If there were no air resistance, how long would it take a free-faz /v/movds;xbg(xt fmdu3 d4 ag8 i35/lling parachutist to fall from a plane at 3200 m to an altitude of 350 m, where she will pull her ripcoru( vs3xtg zfxb ;o/ 8dgm3/4m/v5iaddd? What would her speed be at 350 m? (In reality, the air resistance will restrict her speed to perhaps 150 km/h .)
   s
   km/h

  A fast-food restaurant uses a conveyor belt to send the burgers thrye6vus,eesdh1 8s :w6 , q7qkmough a grilling machine. If the grilling machine is 1.1 m long and the burgers require : ess,q6 6ewy1du,kq me78vsh2.5 min to cook, how fast must the conveyor belt travel? If the burgers are spaced 15 cm apart, what is the rate of burger production (in burgers/min)?
   m/min
   $\frac{burgers}{min}$

  Bill can throw a ball vertically at a speed 1.5 times fas7x55-u0w5 (xi za5w kbmzsac wter than Joe can. How many times higher will Bill’s ball go than Ja55kx(wwaz0umz5s - xw 5c b7ioe’s? $\approx$ =    (retain one decimal places)

  You stand at the top of a cliff while your friend stands on the ground below y 8d u-c)ur-qeyou. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the ground belou- r- dc)uqey8w. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball?    m/s

  Two students are asked to find the height of a particular building using +xt)d +6 eksj e,arwh1 ybci 1;vd*g*za barometer. Instead of using the barometer as an altitude-measuring device, they take it to the roof of the building and drop it off, timing its fall. One student reports a fall time of 2.0 s, and the oev1, *d+dw+ )y egcjhiktsa6r bz;1* xther, 2.3 s. How much difference does the 0.3 s make for the estimates of the building’s height?    m

Figure 2–43 shows the position vs. time graph for 8grlmr y1.: j8eezg .ttwo bicycles, A and B. (a) Is there any instant at which the two bicycles have the same velocity? (b) Which bicy:1zm gt.ger8e r8 l.jycle has the larger acceleration? (c) At which instant(s) are the bicycles passing each other? Which bicycle is passing the other? (d) Which bicycle has the highest instantaneous velocity? (e) Which bicycle has the higher average velocity?